mminer-apple2/src/apple2/level.inc

;-----------------------------------------------------------------------------
; level.inc
; Part of manic miner, the zx spectrum game, made for Apple II
;
; Stefan Wessels, 2020
; This is free and unencumbered software released into the public domain.

;-----------------------------------------------------------------------------
.segment "CODE"

;-----------------------------------------------------------------------------
; "decompress" the stored level into a usable level in levelLayout
.proc levelUnpack

    value    = sizeL
    len      = sizeH

    ldx currLevel

    lda #<levelLayout                           ; point at the level decode area
    sta store + 1
    lda #>levelLayout
    sta store + 2

    lda levelsL, x                              ; get the start of the level data intp srcPtr
    sta srcPtrL
    lda levelsH, x
    sta srcPtrH

    ldx #0                                      ; start at 0 in read and write area
    ldy #0

loop:
    lda (srcPtrL), y                            ; read the first level byte (repeat counts)
    beq done                                    ; $00 ends level
    pha                                         ; save
    iny                                         ; point y at next byte

    lsr                                         ; get high repeat nibble into low nibble
    lsr
    lsr
    lsr
    tax                                         ; but result in X

    lda (srcPtrL), y                            ; read the next byte from level (values)
    sta value                                   ; save
    iny                                         ; advance y to next rep counts

    lsr                                         ; get high value nibble into low nibble
    lsr
    lsr
    lsr
    jsr :+                                      ; store value repeat times into level decode area

    pla                                         ; restore the rep byte
    and #$0f                                    ; only the low nibble
    tax                                         ; put in x
    lda value                                   ; restore values
    and #$0f                                    ; only low nibble
    jsr :+                                      ; store value repeat times into level decode area
    jmp loop                                    ; repeat

:
    stx len                                     ; save the repeat count
    tax                                         ; value into x (value is a tile index)
    lda mult16, x                               ; mult value by 16 as that's how wide a tile is
    ldx len                                     ; restore the repeat count
    dex                                         ; store index is 0+ but count is 1+ so pre-dec

store:
    sta PLACEHOLDER, x                          ; store the tile offset into the level decode area
    dex                                         ; from back to front and
    bpl store                                   ; repeat for all repetitions

    lda len                                     ; get the repeat length
    clc
    adc store + 1                               ; advance the stor pointer by the length
    sta store + 1
    bcc done
    inc store + 2

done:
    rts                                         ; return to self or caller

.endproc

;-----------------------------------------------------------------------------
.proc levelPlaceKeys

    lda #0
    sta keysToCollect                           ; init to 0 keys to collect

    lda currLevel
    asl                                         ; * 2
    asl                                         ; * 4
    adc currLevel                               ; * 5 - index into key table
    tax                                         ; keep index in x

    lda #4                                      ; Need to do 5 keys, 0-4
    sta sizeL                                   ; save count in sizeL
    ldy #0                                      ; keep offst from ptr at 0
:
    lda keyyH, x                                ; get the key Y hi (y=row*32 in key table)
    bmi next                                    ; if $ff then skip
    inc keysToCollect                           ; count the key
    sta dstPtrH                                 ; save the hi
    lda keyyL, x                                ; get the y lo
    adc keyx, x                                 ; and add the x (no carry still)
    sta dstPtrL                                 ; save as dst pointer
    lda #>levelLayout                           ; get the scratch hi (the lo is 0 as it's aligned)
    adc dstPtrH                                 ; and add to the Y hi (and any carry)
    sta dstPtrH                                 ; and save as the dst Pointer Hi
    lda #8*16                                   ; key tile offset * width of a tile
    sta (dstPtrL), y                            ; poke into the unpacked level

next:
    inx                                         ; next key
    dec sizeL                                   ; one less key to do
    bpl :-                                      ; all keys done?

    rts

.endproc